Recently, knock detecting devices that can be used in multiple-stage injection or split injection have been known (for example, see PTL 1). The knock detecting device according to PTL 1 sets a knock determination period to be a base on the basis of an engine ignition time, sets a mask period in accordance with the off-timing of a rear-stage injection of the split injection, and determines whether a knock occurs in a final knock determination period reflecting the mask period. This technique is to separate the on-off-valve noise of the fuel injection valve and the knock by masking the off-timing of the fuel injection from the knock determination period.
Another known knock detecting device (for example, see PTL 2) learns the intensity of the on-off-valve noise caused by the operation of the fuel injection valve when the knock does not occur, calculates a knock determination value on the basis of a learning value of the intensity of the on-off-valve noise, and performs the knock determination.